The present invention relates to implantable medical devices, such as stimulators and leads generally, and more particularly to the fabrication of spiral coil electrodes, spiral stents and other tubal spiral structures.
Currently available implantable ventricular defibrillators typically employ epicardial or subcutaneous patch electrodes, alone, or in conjunction with one or more endocardial leads equipped with one or more electrodes disposed within a heart chamber or blood vessel. Ventricular defibrillation is typically effected with at least one electrode extending along an endocardial lead body disposed within the right ventricle and one or more additional defibrillation electrodes disposed outside the right ventricle to provide two or more defibrillation current pathways through the chamber of the heart to be defibrillated. Other endocardial defibrillation leads for transvenous introduction and positioning in the right atrium and/or superior vena cava, the coronary sinus, the right outflow track or other locations in proximity to the heart have been disclosed in the prior art, including commonly assigned U.S. Pat. No. 4,932,407 to Williams.
Many versions of elongated defibrillation electrodes on a variety of endocardial lead body configurations have also been disclosed in prior patents and literature and employed clinically in patients. The requirements of an endocardial defibrillation electrode include a cross-section size and flexibility sufficient to enable transvenous introduction and withstand chronic flexing in situ. Additionally, a metal alloy exhibiting high bio-compatibility for chronic implantation, low electrical resistance per unit cross-section area of the metal alloy, the capability of providing a relatively large exposed surface area to reduce impedance off the system and distribute the electrical current of the defibrillation shock in a desired pathway in relation to the vessel or chamber of implantation, ease of manufacture, and high reliability are also required. The combination of the selection of materials, design of the electrode configuration and the supporting lead body, and the construction methods employed contribute to achieving these requirements.
After many years of development, the typical endocardial lead defibrillation electrode is configured as an elongated, bio-compatible wire of high conductivity that is spirally space wound or close wound about the lead body for a length appropriate for the intended use. The spacing of the coil turns retains flexibility of the lead body along the length of the electrode and further distributes the electrode surface area along the length thereof. The wire cross-section is typically circular, as shown in U.S. Pat. No. 5,042,143 to Holleman et al., or rectangular, as shown in U.S. Pat. No. 4,481,953 to Gold et al., U.S. Pat. No. 5,090,422 to Dahl et al., and U.S. Pat. No. 5,265,623 to Kroll et al., although other wire configurations, e.g. the wrapped coils of U.S. Pat. No. 5,439,485 to Mar et al., have also been disclosed. The coiled wire electrode may be formed of a single wire or in a multi-filament configuration of interlaced wires as shown in certain embodiments of the ""485 patent. The coiled wire turns are typically partially embedded into the underlying lead body insulation to mechanically stabilize the exposed coil turns and direct t,he defibrillation current outward of the lead body.
In addition, various types of epicardial defibrillation leads having multiple coiled wire electrodes emanating from a common connection or connections with the defibrillation lead conductor have been disclosed as shown in certain embodiments of the above referenced ""422 and ""485 patents and in U.S. Pat. No. 4,860,769 to Fogarty et al., U.S. Pat. No. 4,865,037 to Chin et al., U.S. Pat. No. 4,817,634 to Holleman and U.S. Pat. No. 5,044,374 to Lindemans et al. In the ""634 and ""374 patents, a xe2x80x9cpatchxe2x80x9d lead is depicted having four electrically parallel, branching coiled wire conductors arrayed in a flat supporting patch. The winding pitch of the wire coils is increased in the outermost two branches as compared to the innermost two branches, depicting an arrangement that would have the effect of increasing the electrode surface area along the periphery of the patch, where the current density is typically concentrated in such electrodes.
The exposed defibrillation electrode must be electrically and mechanically attached at one or more points to a defibrillation lead conductor that extends proximally to la connector at the proximal end of the lead body. Typically, the defibrillation lead conductor is a coiled wire conductor, although straight wires of stranded wire filaments are also used. In either case, one end or both ends of the spiral wound defibrillation electrode wire are attached to the lead conductor extending to the proximal end. The attachment(s) require a number of separate parts, and the attachment sleeves, cores and crimps involved may result in a cumbersome and unduly enlarged connection.
As shown in the ""143 and ""485 patents, the coiled wire ends are attached to sleeves by welding, crimping or the like, and at least one of the sleeves is adhered to the internal coiled wire conductor. In the ""953 patent, the ends of the defibrillation electrode wire coil are schematically shown directly connected inside the lead body to the ends of internally disposed straight defibrillation lead conductors. In practice, however, additional parts are needed to make a reliable connection With operable lead conductors.
The ""623 patent discloses the electrical connection of a stranded wire filament cable, defibrillation lead conductor at a central point along the length of an exposed wire ribbon defibrillation electrode. The central connection purportedly alters the electrical field and current distribution of a defibrillation shock applied to the defibrillation electrode with respect to the heart vessel or chamber. The wire ribbon is formed of a continuous rectangular cross-section band wound over a lead body outer insulation sheath in a spiral and between a pair of separate electrode end rings. The separate end rings appear to restrain longitudinal expansion of the wire ribbon electrode.
Further, a commercially available Endotak(copyright) endocardial defibrillation lead is constructed with similar ribbon wire electrode and end caps that are welded to the ends of the wire ribbon. The electrical connection to the defibrillation lead conductor is effected at one or both end caps. The ""623 patent is directed to improving the, electrical current distribution of such an electrode design by decreasing the edge effect current concentrations that can occur at the ends, particularly at the end(s) where the electrical connection(s) to the defibrillation lead conductor is made. It is asserted that such concentrated current densities may damage blood vessels of heart tissue in their vicinity.
A novel approach is disclosed in U.S. Pat. No. 5,728,149 issued to Laske, et al, in which the defibrillation electrode is fabricated of a single tubular member of bio-compatible, electrically conductive material that has the appearance of a band wound around a central point. A plurality of spiral slits is formed in the tubular member thereby forming a plurality of spiral bands integrally attached to the first and second end bands, respectively. The pitch and/or width of the spiral slit bonding including any intermediate connection band may be altered in order to accommodate the electrical connection with the defibrillation lead conductor. This invention, as it relates to the embodiments, requires that the electrical connections may be made directly by welding, crimping or the like to adhere the annular end or intermediate connection band(s) or the intermediate spiral band to the underlying defibrillation lead conductor without any additional parts.
Current fabrication methods to produce the coils in a tubular member include Electron Discharge Machining of the tube stock, coil winding from wire, and milling of the tube stock. These methods are either expensive, design limiting, or alter the natural material properties of the electrode. Other methods include laser or water jet cutting. In both of these fabrication processes, the cutting apparatus is positioned in a superior and central position over the piece to be cut or etched. Because the objective in manufacturing a small diameter implantable electrode is to cut through only one wall of the tubular material, the superior and central positioning of the laser or water jet over the tube makes it impossible to protect the opposite wall from being cut as well. Thus a new approach to the positioning of the jet is necessary.
Accordingly, it continues to be desirable to simplify transvenous defibrillation lead body construction and to make the resulting lead more reliable for long term implantation. Reduction of piece-separate parts and efficient assembly steps in the attachment of the defibrillation electrode with the defibrillation lead conductor are some of the desired features which enhance reliability and quality.
The present invention is generally directed to an improved fabrication process involving the use of a high-pressure water jet to cut or etch in order to form spiral bands in a coiled defibrillation lead. The invention accomplishes this enhancement by strategically positioning and dynamically adjusting a high-pressure water jet to an outside wall of a tubular member. Such positioning allows the high-pressure water jet to make contact only with the proximate outside wall of the tube during the cutting or etching process. This method prevents cutting or etching of the opposing wall of the tubular member. Simultaneous rotation and translation of the tubular member across the discharge path of the water jet enables to form a spiral structure with a specified pitch along the desired length of the tubular member. Etching and cutting such tubes is more economical than creating a coil of drawn wire that must, in turn, be electrically connected to end bands of the coil. Moreover, the high-pressure water jet will riot anneal, warp or otherwise alter the chemical or physical constitution of the material from which the tubular member is made.
The present invention provides a fabrication process for preferably endocardial defibrillation electrodes. This process, however, is not limited to the fabrication of such electrodes and may also be used in the fabrication of implantable spiral stents, spiral structures and similar spring-like homogenous units.